The extracellular matrix influences cellular growth through a complex set of interactions between the matrix and cytoskeleton. Very recent evidence has suggested that the role of cell adhesion in cell growth control is more complex than was first appreciated, an that the structural organization of the matrix, rather than simple adhesion dictates cell cycle progression. Using the amino-terminal matrix assembly domain of fibrinoectin (i.e. the 70 kDa fragment), to affect the organization and deposition in the fibrinoectin matrix in adherent endothelial cells, we have shown that modulation of the fibronectin matrix in adherent endothelial cells, we have shown that modulation of the fibronectin matrix results in the stabilization of the organization of actin phosphorylation of low molecular weight Cas (HEF1) and inhibition of cell cycle progression. Our hypothesis is that the process of fibronectin polymerization regulates matrix based signaling pathways important in endothelial cell growth and that perturbation of the organization of the fibronectin matrix can be used to inhibit tumor dependent angiogenesis. Various recombinant fragments of fibronectin will be used to modulate the homophilic interactions which occur during the polymerization of fibronectin will be used to modulate the homophilic interactions which occur during the polymerization of fibronectin. Each of these homophilic binding events will be compared for their ability to stabilize actin and alter the functional activities of HEF1, a recently identified protein thought to regulate cell growth. Experiments will address whether matrix organization affects the composition of HEF1 containing signaling complexes and their activity of their downstream effectors. Possible downstream effectors of HEF-1 include crk and C5G. The effect of fibronectin fragments on growth factor stimulation of endothelial cell entry into S-phase will be evaluated by determining what steps in G1 are susceptible to modulation by fibronectin organization. Progression through G1 will be assessed by changes in the activity of the cyclin/cdk complexes and expression of genes marking distinct phases of the cell cycle. MCF-7 cells expressing FGF will be infected with retroviral vectors coding for the 70 kDa region of fibronectin to determine whether the 70 kDa fragment of fibronectin can block FGF induced tumor angiogenesis and metastasis in an in vivo model of human breast.